Process of precipitating plutonium and compounds formed thereby



United States Patent y 3 153 614 PRUCESS 0F PRECEPi TATTNG PLUTONPJM AND QOMPQUNDS FGRMED THERE-BY 1 Glenn T. Seaborg, Iiohn E. Willard, and Stanley G.

Thompson, @lricago, IlL, assignors to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed Get. 24, 1945, Ser. No. 624,330

4 Claims. (El. 26t)27tl) Our invention relates to the separation of certain radioactive elements from other radioactive elements and to certain new compounds suitable for use in accomplishing this separation.

It is known that when uranium is subjected to neutron bombardment there is formed in small quantities a new element having an atomic weight of 239 and atomic number of 93, known as neptunium (symbol Np). This new element by radioactive decay is transformed through a half-life of 2.3 days to a further new element known as plutonium (symbol Pu) having an atomic number 94. The particular isotope of this element so produced has a mass of 239. In addition certain other elements are formed as a result of fission of the uranium 235 nucleus such new elements being referred to as fission fragments or, including radioactive decay products thereof, as fission products. The fission fragments are radioactive isotopes which may be included in two general element groups, a light fission fragment comprising elements having atomic numbers from about 29 to 48 such as Br, Kr, Rb, Sr, Y, Zr, Cb, Mo, 43, Ru, Rh and a heavy fission fragment comprising elements having atomic numbers from about I 49 to 65 such as Sb, Te, 1, Xe, Cs, Ba, La, Ce, Pr, and

Nd. The fission fragments are usually present in radio- ?active form, usually having a very short half-life, and by radioactive decay many of the fission products form other short lived products. Thus, the product obtained by neutron bombardment of uranium after more or less aging during or after bombardment comprises a major portion of uranium together with minor portions rarely in excess of one or two percent by weight of fission products and element 94 together with more or less element 93.

The recovery of element 94 in a concentrated form involves the separation of the 94 from such a product without excessive loss of 94.

The removal of fission products from the 94 is of particular interest since some of these retain their radioactivity for a substantial time after the neutron bombardment. Such radioactivity is so intense that it is exceedingly hazardous to personnel engaged in working therewith.

A further problem which is frequently encountered involves the removal of impurities which may be present in a plutonium concentrate in order to secure a more pure product. Such impurities may comprise residual uranium and/or fission products and/ or agents used to assist in the separation of the plutonium from the irradiated uranium and may include numerous light elements including lithium, magnesium, sodium, calcium, silicon, etc.

It is an object of this invention to provide simple and efficient means of separating plutonium from impurities such as neptunium, uranium, light element fission products and other impurities.

It is a further object of this invention to prepare certain "ice new and useful compounds of plutonium which are particularly useful in alfording a method for separating plutonium from aqueous media.

Other objects of this invention will be apparent from the following description.

In accordance with the present invention, it has been found that an effective recovery of the plutonium may be secured by formation of a coordination compound of plutonium with an organic compound containing at least one atom capable of supplying a pair of unshared electrons to the plutonium atom and forming a coordinate or dative bond therewith. In general, it may be said that under modern theories of valence, elements unite with each other in essentially three ways. First, two atoms may unite by virtue of the fact that one atom supplies an electron to the other and this electron is held unequally, i.e., by one of the atoms, whereby one kernel becomes negative with respect to the other. Such a bond is known variously as a polar, heteropolar, electrostatic or an ionic bond. NaCl is a compound having this type of bond. Second, two atoms may unite each supplying'an electron and the electron pair is held equally by both atoms. Such a bond is termed a nonpolar, homopolar or covalent bond. The bond common to most hydrocarbons such as methane, ethane, etc. is nonpolar. The third type of bond is formed when an atom having a pair of unshared electrons shares them with another atom which requires additional electrons to complete its valence shell. Such bond are frequently termed coordinate, coordinate covalent or semipolar bonds.

Atoms or radicals which are capable of forming coordinate linkages include the following:

Thus, the present invention contemplates formation of plutonium compounds from organic compounds which contain one or more of these or similar radicals.

Preferably, the compounds herein produced are obtained from organic compounds capable of forming at least two linkages. Thus, the compounds with which the plutonium is reacted may contain two or more atoms capable of forming a coordinate bond such as above listed. Generally, however, it is preferred to use compounds which are capable of forming at least one ionic or polar bond with the plutonium. Such compounds contain, in addition to the coordinating atom or radical such as listed above, an element or radical capable of adding to metals by a polar bond. Typical radicals of such character include the groups H -COOH, OH, HSO N=o, -NH or NRH Compounds of this type which form complexes with plutonium include the following:

8-hydroxyquinoline and homologues including other hydroxyquinolines which contain the group OH capable of forming a polar bond and a nitrogen capable of forming a coordinate bond;

which contains an enol OI-I capable of forming a polar bond and a coordinating carbonyl group,

Other diketones such as propionyl acetone, propionyl trifiuoro acetone; etc.,

Salicyl aldehyde, in which the aldehyde group is capable of coordination through oxygen;

Ammonium salicylate, also capable of coordination through oxygen;

Benzoyl acetone, capable of combining in a manner similar to acetyl acetone;

Phenyl hydrazine, alizarine and mixtures thereof; condensation products of hydroxy aromatic aldehydes such as salicyl aldehyde with diamines such as ethylene diamine, propylene diamine, etc.; cupferron which is the ammonium salt of N-nitroso phenyl hydroxylamine having the formula,

containing two ketone groups; and isonitrosoacetophenone;

Generally speaking, complexes of the type herein contemplated may be secured from various groups of compounds which contain at least one coordinating atom or group such as listed above and at least one atom capable of establishing a polar bond. Preferably, such linking atoms should be sutliciently close in a chain to permit establishment of a ring which preferably contains five or six members but in general no more than about 8 members. Amino acids such as glycine, alanine, leucine or amino butyric acid or keto acids such as pyruvic acid or acetoacetic acids or nitriles of polycarboxylic acids such as phthalonitrile or partial amides of carboxylic acids such as phthalarnide or oxamide are suitable as well as homologues of the compounds above listed. Moreover, more complex type compounds such as may be prepared by condensing an hydroxy aldehyde such as salicyl aldehyde or homologues thereof with diamines such as ethylene diamine or propylene diamine, may be used to form complexes with plutonium.

Water soluble complexes of plutonium may be produced where the organic radicals contain water so-lubilizing groups such as sulphonic acid or sodium acid sulphate groups. For example, sulphonates of hydroxyquinolines such as 7-iodo-S-hydroxyquinoline-S-sulphonic acid may be complexed with plutonium to form water soluble complexes.

Complexes which are especially suitable for the purpose herein contemplated may be secured from organic acids which contain a coordinating atom. Such acids may be carboxylic acids or may contain other acidic groups such as the acidic hydroxy aromatic compounds. Most suitable of such acids are those which contain a trivalent coordinating nitrogen atom. Such acids form plutonium complexes wih unusual case.

The process is particularly effective when applied to reaction of the complexing compound with plutonium in the tetravalent state. However, these complexing agents form complexes with trior hexavalent plutonium, and generally such complexes are not distinguishable by present methods from the product obtained with tetravalent plutonium.

Generally speaking, the complexes herein contemplated may be secured by reaction of a plutonium salt,

a such as a plutonium nitrate, in aqueous medium with the organic compound. Usually the reaction can be effected at room temperature while agitating the mixture over a suitable period of time, for example, 48 hours. The compounds so obtained may be precipitated or extracted with organic solvents or recovered by other convenient means. Where small quantities of plutonium are being handled, extraction is generally the more suitable method of recovery.

The exact structure of the compounds obtained is not known. Generally, they are solids which are frequently highly colored. The complexes appear to be cyclic compounds of the chelate type. For example, the plutonium complex obtained from tetravalent plutonium and Shydroxyquinoline appears upon analysis and test to have the following probable formula:

Similarly, the plutonium complex formed from cupferron andtetravalent plutonium appears on investigation to have the following structure:

0 J, O P

The production of these complexes is extremely useful in affording a means whereby plutonium may be separated from impurities such as are present in neutron irradiated uranium or from light metals. Thus, neutron irradiated uranium may be converted to a water soluble state and dissolved to form an aqueous solution, for example, a nitrate solution. This solution may be treated to separate uranium from the plutonium. A suitable method involves adsorption of the plutonium from the uranium in which case a major portion of the fission products are removed with the plutonium. For example, a solution of irradiated uranyl nitrate may be treated to selectively reduce the plutonium to a lower valent state,

the organic solvent as a suspension or precipitate.

understood throughout this specification and claims that generally the tri or tetravalent state by means of a suitable reducing agent. Lower Valent plutonium (Puor Pu' may be oxidized to the hexavalent state by an oxidation potential of about 1.1 volts. Reduction of the plutonium to the lower valent state may be effected by reducing agents which are listed above 1.1 volts in the Latirner and Hildebrand table of oxidation-reduction potentials.

To secure a selective reduction of plutonium without excessive reduction of uranium, reducing agents having a reducing potential which is sufiiciently low as to be unable to reduce hexavalent uranium are used. Suitable agents to accomplish this result include ferrous ion, uranous ion or hydroxyl amine hydrochloride.

The solution containing reduced plutonium is then treated for removal of plutonium by contacting the solution with an adsorbent such as columbic oxide (Cb O silica gel, bismuthphosphate or resinous condensation products of phenol sulphuric acid and formaldehyde or by precipitating a carrier, such as bismuth phosphate or lanthanum fluoride in the solution. in such a process, the adsorbent or carrier removes plutonium in reduced state together with some quantity of the fission products. The plutonium is then removed from the carrier or adsorbent by dissolving or extracting with an acid, particularly an inorganic acid, to form an acid solution such as nitric acid solution containing 5 to percent HNO A suitable description of such a process appears in an application of Stanley G. Thompson and Glenn T. Seaborg, Serial No. 478,570, filed March 9, 1943, now Patent No. 2,799,553, granted on July 16, 1957.

The resulting solution contains plutonium, fission products, some uranium and more or less of the ions of the adsorbent. The plutonium or a substantial portion thereof may be removed by formation of a water insoluble organic complex such as herein described. These complexes are then precipitated or extracted with a solvent such as chloroform, benzene, carbon tetrachloride, aniline, 11 hexylalcohol, xylene, ethyl ether or other water immiscible organic solvent. The water immiscible organic solvents as used in the process of the present invention extract the plutonium organic complexes from aqueous solutions either by actual solution in the solvent or by preferential wetting by the solvent. In the case of preferential wetting, the plutonium complex may appear in It is extraction by the solvent includes extraction by solvent action and/ or by preferential wetting.

The formation of the complex to be so precipitated or extracted may be effected by adding the complexing organic compound to a plutonium solution which may contain uranium and/ or the fission products and permitting the mixture to stand usually with agitation for a substantial period of time, for example, 48 hours. Usually heating is unnecessary although it may be used if desired to expedite the reaction where it does not cause decomposition of the complex. Frequently, the complexes are found to form more readily at certain preferred pH values usually on the acid side and in such a case, the pH of the solution is adjusted to the desired value. In general, it is preferred to avoid the use of strongly acid or strongly basic solutions, and usually the pH is adjusted to be within a range of about 1 to 8 the specific value depending upon the complex to be formed. For example, certain agents such as isonitrosoacetophenone or dibenzoyl methane form complexes more readily at a pH of about 8. Others such as the condensation products of hydroxy benzaldehydes and alkylene diamines are more effective at a pH of 3-5.

The present invention is illustrated by the following examples.

EXAMPLE I An excess of a 2 percent solution of S-hydroxyquinoline and acetic acid was added to a solution containing from 1 percent to 0.1 percent neutron irradiated uranyl nitrate hexahydrate, UO (NO .6H O, and hexavalent plutonium and neptunium in tracer quantities. The pH of both solutions was adjusted to the value desired, shown in the table below, and the pH after the mixing and precipitating was determined. Following precipitation, the supernatant liquid and a nitric acid solution of the precipitate were analysed for plutonium and neptunium by counting the alpha and beta particles from samples of the precipitated fluorides. Results are shown in the following table:

Table 1 Percent Percent Exp. N0. pH Pptn. Holdback of 94 of 93 carrier carrier pptd. pptd 3.2 UO2++ Ce+ Ce' 3.3 UOz++ Oe-l Gel- 87 6 3.9 UOz-k None 98 4.3 UOz-l-l. (Jed- Ce+ 97 12 Due to extremely small quantities involved, it was necessary to use precipitation carriers and hold back carriers. Precipitation carriers are substances which precipitate under the conditions used and carry with them the minute quantities of plutonium being precipitated. Such minute quantities of plutonium might not otherwise completely precipitate out in separable form. The holdback carriers are to prevent precipitation of some substances such as radioactive fission products which might otherwise precipitate along with the plutonium and the precipitation carrier. Such holdback carriers generally effect this result by precipitating in lieu of the fission product.

In all of the runs some precipitation of uranyl quinolate was formed. 0.3 mg. portions of cerium ion, Ce+ and Ce, were used as holdback carriers in runs No. 1, 2 and Uranyl ion, U0 in the solution served is the carrier. One additional run was carried out with no neptunium present and this showed UX is approximately 63 percent precipitated from 0.5 percent, uranyl nitrate hexahydrate, U0 (NO .6H O, solution by S-hydroxyquinoline at a pH of 4, with no holdback carrier present.

The results of the runs appearing in Table 1 show that substantially all of the plutonium is separated from neptunium by the use of S-hydroxyquinoline as the precipitant.

EXAMPLE 2 In order to test the tendency for various light elements to follow the plutonium complex into organic solvent solution, the separation factor for a number of light elements has been determined. The light elements tested were aluminum, beryllium, calcium, iron, lithium, magnesium, sodium and silicon.

The separation factor is defined as the fraction of a given element that follows the plutonium complex into the organic solvent, i.e., it is the ratio of the amount of the light element in the organic solvent after extraction to the amount of the same element originally present in the aqueous solution. In each of the following experiments, 0.5 milliliters of an aqueous citrate solution of the plutonium complex formed by adding the ccmplexing reagent to the solution of plutonium citrate buffered to a pH of approximately 7. This solution which contained about 400 micrograms of tetravalent plutonium was extracted with an organic solvent. The aqueous solution in each experiment had added to it approximately two micrograms of each of the light metals tested. The aqueous solution in each case was shaken with an equal volume of solvent and over 90 percent of the plutonium was extracted. Following the extraction, the light element present in each phase was determined spectrographically. The separation factors found are shown in the following table. In the table L means less than.

Table II Reagent used to form Separation Factors in Units of 10- plutonium organic Solvent complex Al Be a. Fe L1 Mg Na S1 Quinaldinic acid 200 L40 200 L5 L4 4 L B-Hydroxy-quinol' L200 10 10 L10 L10 L40 Salicylaldoxime. 100 200 10 200 200 L10 Salicylic Acidfls 10 L200 10 L2 L10 40 Salicylaldohyde... 100 5 100 L2 1 10 4 2 cc. of a nitrate solution containing 1.019 milligrams of plutonium and having a pH of 4 was shaken up with 17.7 milligrams of 2,3-dihydroxy, S-tertiary butyl benzal ethylene diamine (prepared by condensing the 2,3-dihydroxy, S-tertiary butyl benzaldehyde with ethylene (diamine) with a few drops of acetone. The mixture was stirred periodically over a period of 48 hours during which the solution changed in color from yellow orange to chocolate brown. The mixture was then extracted with chloroform and 98 percent of the plutonium recovered in the chloroform layer. The complex so produced is a chocolate brown solid which is substantially insoluble in water but which is soluble in organic solvents such as toluene or chloroform.

Other complexes of a similar character may be secured by use of other diamines such as propylene diamine derivatives in lieu of ethylene diamine derivatives.

Although the present invention is particularly concerned with the production of compounds or complexes of the isotope 94 it is broadly applicable to the production of compounds and to the recovery of element 94 including all isotopes thereof. bombardment of uranium results in formation of the isotope 94 Other isotopes of this element may be formed upon subjecting uranium to prolonged thermal neutron bombardment of high intensity. All such isotopes may be recovered as herein contemplated.

Although the present invention has been described with particular reference to the specific details of certain embodiments thereof, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

We claim:

1. The process of separating plutonium from impurities that comprises forming an aqueous solution of plutonium with the impurities, adding 8-hydroxyquinoline to the solution and separating and recovering the plutonium 8-hydroxyquinolate.

2. The process of separating plutonium from impurities For example, neutron that comprises forming an aqueous solution of plutonium with the impurities, adding a hydroxyquinoline to the solution and separating and recovering the plutonium hydroxyquinolate complex.

3. An organic chelate complex of 8-hydroxyquinoline and plutonium.

4. A process of separating plutonium values from impurities present together in an aqueous solution, comprising adding to said aqueous solution an organic compound selected from the group consisting of 8-hydroxy-quinoline, quinaldinic acid, salicylaldoxime, salicylic acid, salicylaldehyde and 2,3-dihydroxy, S-tertiary butyl benzal ethylene diamine, whereby a chelate complex is formed between said organic compound and said plutonium values, and separating said chelate complex from the aqueous solution.

References Cited by the Examiner UNITED STATES PATENTS 2,837,548 6/58 Spedding et al. 260-4291 2,863,892 12/58 James ct al. 260429.l 2,868,817 1/59 Potratz 260-429.1

OTHER REFERENCES CARL D. QUARFORTH, Primary Examiner.

ROGER L. CAMPBELL, JAMES L. BRENRINK, A. W.

CROCKER, Examiners. 1 

3. AN ORGANIC CHELATE COMPLEX OF 8-HYDROXYQUINOLINE AND PLUTONIUM.
 4. A PROCESS OF SEPARATING PLUTONIUM VALUES FROM IMPURITIES PRESENT TOGETHER IN AN AQUEOUS SOLUTION, COMPRISING ADDING TO SAID AQUEOUS SOLUTION AN ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF 8-HYDROXY-QUINOLINE, QUINALDINIC ACID, SALICYLADOXIME, SALICYLIC ACID, SALICYLALDEHYDE AND 2,3-DIHYDROXY, 5-TERTIARY BUTYL BENZAL ETHYLENE DIAMINE, WHEREBY A CHELATE COMPLEX IS FORMED BETWEEN SAID ORGANIC COMPOUND AND SAID PLUTONIUM VALUES, AND SEPARATING SAID CHELATE COMPLEX FROM THE AQUEOUS SOLUTION. 